Other Vinyl Polymers
Polyethylene may be considered either as -n- with a repeat unit of --, or as n-, with a repeat unit of --. Chemists tend to consider the repeat unit as -- since this polymer is made from the monomer ethylene (CH2=CH2).
More complex repeat units can occur in vinyl polymers -n-, if one hydrogen in the ethylene repeat unit is substituted by a larger fragment R. Polypropylene -n- has the repeat unit -. Polystyrene has a chain where the substituent R is a phenyl group (C6H5), corresponding to a benzene ring minus one hydrogen: -n-, so the repeat unit is -n-.
Read more about this topic: Repeat Unit